.
Let a = amount paid by A
b = by B
c = by C
d = by D
e = by E.
Then
a = (1)
b = (2)
c = (3)
d = (4)
Multiply equations: (1) by 3; (2) by 4; (3) by 5; and (4) by 6. The modified system is
3a = b + c + d + e (5)
4b = a + c + d + e (6)
5c = a + b + d + e (7)
6d = a + b + c + e (8)
Add "a" to both sides of (5). Add "b" to both sides of (6). Add "c" to both sides of (7), Add "d" to both sides of (8).
Use the fact that a + b + c + d + e = 42000. You will get
4a = 42000 ====> a = = 10500. (9)
5b = 42000 ====> b = = 8400. (10)
6c = 42000 ====> c = = 7000. (11)
7d = 42000 ====> d = = 6000. (12)
Then a + b + c + d = 10500 + 8400 + 7000 + 6000 = 31900,
and e = 42000 - 31900 = 10100.
Answer. E payed 10100.
Solved.